Filament



Dec. 17, 1940. Q SPAETH 2,225,239

FILAMENT Original Filed Aug. 14, 1956 W XML m f ww Patented Dec. 17, 1940 UNITED s'r'ATEs azzaza)A FILAMENT Charles Spaeth, Flushing, N. Y.

Original application August 14, 1936, Serial No. 96,040. Divided and this application April 18, 1939, Serial NO. 268,571

11 Claims.

This invention consists in a non-sag filament of tungsten' wire for use in incandescent or other electric lamps. This application is a division of my application Ser. No. 96,040 now Patent No. 2,165,310, granted July 11, 1939, in which the process of making the new filament is disclosed.

and claimed.

Tungsten wire filaments as heretofore con-| structed, especially of the coiled coil type, have required special treatment to prevent sagging due to crystaliine displacement when operated at the temperature of incandescence in electric lamps. Th'e treatment formerly necessary has required heating of the filament Wire at a temperature between 1600 and 1700 C. in order to'settle the tungsten crystals permanently in sha'pe. Such treatment has been diflicult because furnaces capable of Operating at such high temperatures have a short life and are not readily available as commercial equipment.

Other expedients relied upon in producing non-sag tungsten filaments have required the use of additives such as thorium oxide, rare earth metal oxides, rare earth metal nitrides which are expensive to procure or require considerable skill and experience in working.

I have discovered that a satisfactory non-sag filament may be produced from subst'antially pure tungsten wire or commercial tungsten Wire by certain steps of procedure which obviate the diiiiculties above discussed. In accordance with the process of my invention the structure of the a tungsten Wire is reinforced by forming a ferrous, nickel or other reinforcing alloy in the Wire. This may be readily efiected by a series of steps well adapted for processes of commercial manufacture and at little expense and may be advantageously. combined with a heat treatment of the filament 4wherein a preliminary and lpartial settling of the crystallinestructure of the tungsten is eifected at a temperature of about 1000 to about 1300 C.,.followe d by a final heating at higher temperature after the filament has been mounted permanently in the lamp in which it is to serve.

Ihave found it possible to produce a tungsten Wire' filament having a satisfactory crystaliine :Tdjustment of the tungsten wire by subjecting the filamentl for an interval of from 1 to 10 minutes to a temperature of about 1000 to about heated to a temperature below the temperature used in the previous firing in the furnace and then rapidly raised 'to a temperature, for example, of approximately 2700 C. for a 100 to 500 watt filament. At about this temperature the 5 final or complete settling of the crystaliine structure takes place whereas for filaments of smaller capacity a somewhat lower temperature will suffice. i

Preferably the preliminary heating 'is carried out in an atmosphere of nitrog'en, hydrogen or other non-oxidizing gas and in the presence of iron, nickel or some other element having a lower melting point and a higher vapor pressure than tungsten. Under such circumstances a small 16 amount of the iron or other metal is vaporized and deposited upon surface portions of the filament. The low melting point metal may be present as a core upon which the tungsten wire` is wound with suitable mandrel and pitch ratios in 20 order to produce suflicient preliminary strains in the tungsten wires and mandrei wires during the coiling Operations in coiling single, or coiled coils or triple coils and upon which is deposited simultaneously with the preliminary step of the heat treatment, an iron or other metal film. Iron may also be made available being electrolytical deposition or may be plated upon the surface of the tungsten Wire by any satisfactory plating process.

As a practical matter it is convenient to deposit a slight excess amount of iron or nickel'uponthe lsurface of the tungsten Wire. and the surplus may be subsequently removed by a suitable acid solvent. If an iron or nickel core has been emi ployed, this may be dissolved at the same time and only so much iron is left in the filament as has entered into the molecular interstices of the a tungsten structure. i

The filament is completed by subjecting it to steps which complete the settling of the tungsten 40 c -Jstals and cause the iron or nickel or other metal to be interalloyed with. the tungsten. These two changes of physical characteristics o may be eifected by mounting the filament in the lamp in which it is to be finally used. then rais-' ing the filament to a temperature slightly below that at which the previous' heating step left off, and finally rapidly raising the temperature o f the filament to lapproximately 2700*' C. This 'may be conveniently effected by placing the filament w in electric circuit, first at a potential of about 20 volts, and then raising the potential rapidly to approximately 120 volts; under which condition' the filament is raisedto incandescent and goes through the changes above discussed, however,

. with special advantage for use as a triple coil illament of the general character disclosed in my co-pending application Ser. No. 15,605. flledV April 10, `1935. The fact that the `process of` making the filament of my invention, in settling or stabilizing the structure of coiled coil illaments. requires lower temperature 'in the heat:`

treatment of the metal compared to other previously known processes of making coiled coil illa-` ments using molybdenum Wire mandrels, makes the filament wire less brittle than heretofore.

`'Ji'he addition of the reinforcing alloy of iron. or the like reduces the rate of vevaporation of the tungsten and thisin turn reduces the tendency of blackening the bulb by vaporized deposit from the filament and therefore results in a better lumen maintenance than it has beenpossible to secure from lamps heretofore known.

These and other features of the invention will be best understood and appreciated from the following description of a preferred embodiment thereof and of one manner in which the process may be carried out, as illustrated inthe accompanying drawing, in which- `l1 p i Fig. 1 is a sectional view. somewhat diagrammatical in form. of a furnace with a number of iilament blanks in process of treatment therein,

Fig. 2 isa diagram suggestive of the electrical heating step of the process, i

Fig. v3 is a view in perspective showing a mounted coiled filament.

Fig. 'i is a view in elevationon a greatly enlarged scale of a portion of a triple coiled illa-` ment, and

Fig. 5 is a sectional view on a still larger scale showing a filament coiled upon its mandrel and` coated with an iron deposit shown in a somewhat exaggerated diagrammatical form. v

The fllament with suitable mandrel ratios and In preparing a double or for example a Vtriple coiled filament the tungsten wire 3| may be first coiled cr twisted about a tungsten mandrel wire 30 to form the primary coil, as shown in Fig. 4.'

The primary coil may then be coiled about an iron mandrel to form secondary coils 32 and the secondary coils, with the enclosed mandrels, may be coiled vabout another iron mandrel to form tertiary coils 33. A coil of this character is illustrated in Fig. 4.

Having shaped the fllament as above outlined, a number of the fiiament blanks lt, after` the conve tional cleaning process, are placed intray I3 and inserted in a high temperature furnace, such f r example asthat illustrated in Fig. 1. This f 'nace is one of a type which is commercially vailable and comprises an outercasing III in which is placed a mume ll of` alundum or otherporous and highly refractory material. A heating coil |2 for the muiile is conventionally represented in Fig. l. The casing Ill is provided with an` inlet pipe H at the upper left hand corner and with an outlet pipe IS at its lower right hand corner by means of which non-oxidizing gases, such as nitrogen or hydrogen, or

If a fllamentof the single coil` type is required, tungsten wire 4| may be coiled about an iron mandrel |0 as suggested in Fig. 5.

v` aaaaaso mixtures may be supplied to the fumaoe so that the heat treatment of the fllament blanks may 'be carried out in a non-oxidizing, inert atmosphere. 4It will be understood that the material of` the mume ll is sumciently porous to permit the gas to permeate it. The iilament blanks |8 in= single, double or triple coiled form are laid side by side in a tray ll of molybdenum or material which is not` affected by the temperature of the furnace.

Having placed the -fllament blanks ll in the furnace as above explained the temperature of the furnace is raised to a `temperature between about1000 and about 1300*' C. and the fllament blanks subiected to this temperature for a period of about 1 to 10 minutes in an atmosphere of nitrogen orfhydrogenpreferably which has i been passed through a water bath so that it has picked up some moisture. As=already expLained this step of thevprocess may be carried out. in a commercial furnace `readily ;available and havoutlined. v i It will be noted that during this step of the treatment the `tungsten wire iswound Vupon a `ing a long life under`` the circumstanees of use core of iron, nickel orthe like, of a lower melting i point and a higher vapor pressure than` the to state here that during this step of the treat'` ment the amount of vaporized core material represents'a very small part of ,the total mass of the tungsten wire or iiiament. i i

The heat treated `blanks. are now removed from the furnace and allowed to cool. They are then` immersed in a suitable acid, for example hydrochloric for iron, and the iron core or cores mounted as suggested in Fig. 3. In this figure the coil filarnent 20 is shown as supported by` hooks above the end of a glass rod 2| which pro-` jects from the press 23 of the lamp. Lead wires 22 are sealed into the press 23 and connected to the ends of the fllament. The filament with its mount is sealed into a lamp bulb, not shown, in the usual manner, the bulb is exhausted and fllled `with'argon gas, an argon-nitrogen mixture or the like and then connected in electric circuit;` The filament is now electrically heated to a temperature somewhat below thatat which the preliminary heat treatment left off, i. e. ap-

proximately to l200 C. If the filament is intended for an volt lamp the initial voltageof the circuit lmay be 20 volts as suggested in Fig. 2, and in any' case ,lan `initial voltage is used which will produce the desired heating condi tion, however, if desiredithe full 120 volts can be applied to the lamp immediately. i

Having brought the iilament to an initial temperature of approximately l200 C. the voltage is raised gradually and progressively to a point at which the illament is heated to approximately pected. For example, in treating pfilaments forl 2700 C, at' which temperature aw complete 'settling of the crystalline structure takes place and also a complete alloying of the ironor nickel or other metal film with the tungsten of the filament. This final heat treatment, of thecoll may lbe'eifected in a period of about one secondto about one minute as 'suggested in Fig. 2.

Fig. is suggestive of the alternative step of electrolytically providing the coiled filament with a coating of iron, nickel or the like. In this' instance the tungsten Wire 4| coiled upon a,

mandrel 40 is immersed in a solution of ferrous chloride and sodium tungstate and placed in an electric circuit as the cathode of a plating system. The iron from the solution Vis thus deposited in a film or coating 42 upon the core 40 and the coil 4|. Subsequently the thickness of the coatlng may be reduced to a surface film, or merely to traces of iron in the surface structure of the tungsten, and it is this iron which is subsequently alloyed with the tungsten by the heat treating steps above set forth.

It may be noted that if an ordinary coiled coil filament is heated to about 1000 to 1300 C. and the mandrels on which it was wound are dissolved by an acid, the coil does not maintain its i shape but is likely to alter in pitch, turns per inch, internal diameter, etc., because the temperature to which it has been subjected is too low to settle the crystalline structure of the wire.

In order to accomplish settling of ordinary coiled coils with molymandrels, temperatures of 1500 C. to 1800 are required, hence the use of molybdenum Wire mandrels instead of iron mandrels. The result is that under these circumstances the coil will uncoil itself partially and acquire a distortecl Shape. The process of my invention as above described is fully effective in settling the crystalline structure of the tungsten so that the coils will maintain their form as originally determined by the coiling machine and all this is effected without requiring a furnace treatment of over 1300 C.

Among the numerous advantages of the filament of my invention is that it is more ductile and less brittle than illaments of this kind heretofore known. When the crystalline structure of a tungsten filament is stabiliized at a temperature of l600 to 1700 C. it is rendered'brittle to an extent that causes an objectionable amount of breakage due to vibration in handling, in mounting, or in shipment. The preliminary heat treatment at lower temperature, followed by the final treatment at higher temperature in accordance with my novel process results in a more ductile product well adapted to withstand the shocks and vibrations of handling and shipping.

Another important advantage is in increased life of the filament. This is due to the fact that lthe metal alloyed with the surface of the tungsten wire substantially reduces the rate of vaporization of the filament material in use. This not only reduces waste from the filament itself but reduces blackening of the bulb and .thus increases the useful life of the lamp to a marked extent as well as its bum-out life compared on a basis of equal initial efliciency in lumens per watt with lamps heretofore known.

I have described my invention having in mind particularly filaments for 100 to 500 Watt lamps and while the temperatures and time intervals mentioned are satisfactory for the treatment of such filaments, it will be understood that some Variation in these respects is permitted and exsmaller lamps a final temperature `of 2000 to 2400o C. may be adequate in the finished lamp. The time of treatment moreover may vary from a few seconds to several minutes depending somewhat upon the size of the filament being treated.

While it is desirable in general to carry out` the heat treatment of the filament in a nonoxidizing atmosphere, it may be advantageous in some cases to include a small amount of water vapor, particularly for the purpose of removing any graphite lubricant' which may be present upon the surface of the tungsten Wire. If water vapor is present it is decomposed into hydrogenl and oxygen and the oxygen will immediately combine with any traces of graphite present on the Wire forming carbon monoxide or carbon dioxide which are washed out ofthe fumace by the hydrogen. This not only cleans the wire but prevents the formation of surface carbides which tend to make the filament brittle.

Having thus described my invention, what IV claim as new and desire to secure by Letters Patent is:

1. A filament for an electric lamp comprising a tungsten wire coiled in helical form and permeated by an interalloy of iron produced by flrst coiling the tungsten wire upon an iron core, then heating to cause some iron fromv the core to become deposited upon the coil, then dissolving the core, and finally heating to cause the remaining iron and tungsten to become alloyed.

2. A filament comprising a tungsten wire coiled in helical form and permeated by an interalloy of iron imparting non-sagging characteristics to the helix and produced by heating the coiled helix on an iron core simultaneously to efl'ect a partial settling of the crystalline structure and to cause the deposition of iron upon the surface of the wire, cooling the filament, removing the iron core, and then heating it sufliciently to effect a further settling of its crystalline structure and to cause the iron thereon to become alloyed with the tungsten.

3. A coiled ductile filament for a 110 volt to 120 volt lamp, comprising tungsten wire coiled into a helix and permeated by an interalloy of iron and produced by coating the coiled helix with iron,

heating it to a temperature between 1000 C. and

1300 C. allowing it to cool, removing the excess iron, and then electrically heating it by including it in a circuit wherein the potential is raised from approximately 20 volts to approximately 120 volts.

4. A filament comprising tungsten Wire coiled into a helix and permeated by an interalloy of the iron-nickel group and produced by depositing a surface film of a metal of the iron-nickel group upon the coiled helix, heating the coated helix to a temperature between about 1000 C. and 1300 C., cooling the helix, removing the deposited metal, then again heating it to approximately' 1200 C., and finally raising said temperature to above 2000 C., thus imparting a non-sagging character to the filament.

5. A filament comprising a tungsten Wire coiled into a helix and permeated by an'lnterallo'y of ferrous metal, the filament having beenproduced byV winding the tungsten wire on al core of ferrous metal having a lower melting point and a higher vapor pressure than tungsten, firing the coil to cause some of the core metal to vaporize core, and finally heating to a temperature ailoying the two metals together.

6. A non-sazgingvfilament comprising tunasten H i wire coiled in the form/of a helix and permeated by an interalloy of ferrous metal, a'nd produced by coatinx the coil with ferrous metal of a lower melting point and higher `vapor pressure than tungsten, heating the coated helix toa temperature of about'1000` to about 1300C.. allowinx the helix to cool and then alloyinx saidl metal and tungsten by including the helix in an electric circuit wherein the potential is suflicient to heat the `wire thereof to about 2000 to 2700*? C.`

7. A coiled coil filament for electric lamps comprising a tungsten wire coiled in the form of primary and secondary helices and .permeated with an interalloy of ironfand produced by windi ing` the wire upon a tungsten core 'in a primary helix, winding the primary helix with its core upon an iron core, heatingto cause some iron from the iron core to become deposited upon the tungsten Wire of the filament, removing the iron core, and then further heating to cause the remaining iron to become alloyed with the tungi sten Wire.

8. A ductile non-sagging filament cornprisingv a` tungsten Wire coiled in theform of primary and n 9. Arnon-saaaina diament comprisinz a tunzsten Wire coiled in the form of primary and secondary helices and permeated by an interalloy of iron, and produced by windinathe tunasten wire upon an ironV core to form a primary helix. windins said helix` with its coren'upona second iron core, heatinz to causesome iron from 'the iron cores to'be deposited upon the tunasten wire helices thus formed,'removing both the iron cores, and then further heatinz .to vcause theiremaininz iron to become alloyed withtthe tungsten wire of the helices. i i

10. A ductile non-maine diament comprislng a tungsten wire coiled in the form of primary and secondary helices and permeated by an interalloy of a ferrous metal and produced by `windiniz the tungsten wire upon a ferrous metal; core to form a primary helix, windina said helix tvith its core upon a second ferrous metal core, heating to cause metal from the cores to be dcposited upon the tungsten wire helices ``thus formed. removing both metal cores, and then further heatinz` to cause the remainina :metal t to become ailoyed with the tunzsten wire.

11. A coiled coil nlament for an electric lamp comprising a tungsten wire coiled in the form of primary and secondary helices and permeated by an interalloy of metals of the nickel-iron group. produced by `coiiing the tungsten wire upon metal cores of the nickel-iron `group,` then heating to cause some metal from the cores to become deposited upon the wire to effect simultaneousiy a partial settling of the crystalline structure of the tungsten wire, removing the metal cores, and then heating it sufliciently to effect a furthcr set' tling of its crystalline structure.

CHARLE sPAE'rH. 

